Shear and tensile reinforcement for inflatable bolt

ABSTRACT

An inflatable rock bolt including an expansion tube, a bushing arranged at each end of the expansion tube, and at least one reinforcing member arranged outside the expansion tube. The at least one reinforcing member includes at least one of a strand extending along the expansion tube or a sleeve at least partially surrounding the expansion tube. A method for reinforcing an inflatable rock bolt.

FIELD OF THE INVENTION

The invention relates inflatable rock bolts. In particular, the invention relates to reinforcement for inflatable rock bolts. The invention also relates to a method for reinforcing an inflatable rock bolt.

BACKGROUND OF THE INVENTION

Rock is removed from the ground in a number of contexts, such as in mining and tunnel construction. Voids, or cavities, are created by the removal of the rock. Underground voids formed by removing material leaves walls and ceilings of surrounding rock. The remaining surrounding rock is subject to gravity and without the removed material to support the surrounding material may tend to converge. Convergence is the decrease of tunnel size caused by gravity and relieving residual ground stresses. Controlling convergence is a critical safety activity.

One technique for controlling convergence includes drilling holes in the surrounding material and anchoring bolts in the material to reinforce and stabilize the material. Rock bolts are anchored between stable rock deep in the hole and the surface of a void. Together, the bolts act as a field of tensile bridges that, to a certain depth, prevent the surface from fracturing and falling into the void.

If ground convergence exceeds the elongation limit of any of the rock bolts, they will fracture. If a bolt or group of bolts fail and no longer constrain a given mass of rock, that mass will fall into the void with the potential to cause injury or death and property damage.

One group of rock bolt anchors is referred to as the inflatable rock bolt. Swellex is the trademarked Atlas Copco brand and is the original of this family of ground support anchor. The inflatable rock bolt is comprised of a long, folded tube welded to an end bushing and inflation bushing at each of its ends. High-pressure fluid is pumped through a small hole in the inflation bushing and inflates the folded tube inside a bore hole and tightens the tube against the wall of the hole, creating a friction and mechanical lock. The bushing at one end may extend through a plate included at the rock face. The length of an inflatable bolt may be determined by structural requirements of the tunnel design.

Though this device has high tensile capacity and installation time is low, one drawback is that the shear strength and stiffness of the inflation tube may be poor compared to other ground control devices that use solid profiles and grout and/or resin to create the bolt/ground interlock. The low shear strength may be at least in part due to the thin walled material utilized to form the inflatable element(s). However, it is inherent that an inflatable material is thin to have the ability to be inflated and create a compression field in surrounding rock and a friction interface along its length.

One attempt to reinforce an inflatable bolt includes a reinforcing member inserted into an inflatable bolt. However, there are a number of shortcomings associated with such an arrangement. For example, an inflatable bolt has a small interior cross-sectional area in which a reinforcing member may be inserted. This will make it difficult to insert and accommodate a reinforcing structure within the inflatable bolt, particularly if the reinforcing member is round.

Additionally, inflatable bolts have a complex shape that is formed in many stages. This makes it difficult if not impossible to form the bolt around the reinforcing structure, particularly for high volume production. Additionally, inserting a reinforcing member within the inflatable bolt would be difficult if not impossible, due to the length of the bolts. For example, the reinforcing member could easily be jammed within the bold during insertion, leaving it only partially inserted.

Furthermore, securing a reinforcing member inserted into an inflatable bolt would be difficult. For example, the ends of the bolts are pinched by bushings, which are a few inches long. As a result, the reinforcing structure would need to be welded to the interior of the bolt. This would be impractical or impossible for welding equipment to be inserted into the bolt. If the reinforcing member is heat treated or hardened, tempering would be required before welding for the weld to hold. The chemical composition of hardened material does not react well to the welding process.

If a reinforcing member were inserted into an inflatable bolt, the reinforcing member could also block the inflation port. As a result, the bolt would not inflate properly. Since the bolt would be inserted into a hole at this stage, the installer would have no indication that the bolt is not properly inflated.

Still further, the reduced surface area of the bolt to accommodate the reinforcing member would reduce the force the bolt applies on the bore hole. This would lower the bolt's grip on the rock. If the bolt surface area were maintained, the reinforcing member would be too small to make a significant increase in the bolt's performance.

SUMMARY OF THE INVENTION

Embodiments of the invention include an inflatable rock bolt including an expansion tube, a bushing arranged at each end of the expansion tube, and at least one reinforcing member arranged outside the expansion tube. The at least one reinforcing member includes at least one of a strand extending along the expansion tube or a sleeve at least partially surrounding the expansion tube.

Additionally, embodiments of the invention include a method for reinforcing an inflatable rock bolt. The method includes extending at least one reinforcing member along an exterior surface of an expansion tube. The at least one reinforcing member includes at least one of a strand extending along the expansion tube or a sleeve at least partially surrounding the expansion tube. A bushing is arranged at each end of the expansion tube. The expansion tube and at least reinforcing member are inserted into a hole. The expansion tube is expanded, thereby frictionally clamping the at least one reinforcing member between the expansion tube and a wall of the hole in which the bolt is inserted.

Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings, in which:

FIG. 1 represents a perspective view of an embodiment of an inflatable bolt and reinforcing structure;

FIG. 2 represents a transverse cross-sectional view of embodiment of an inflatable bolt and reinforcing structure;

FIG. 3 represents a longitudinal cross-sectional view of the embodiment shown in FIG. 2 along the lines 3-3;

FIG. 4 close-up perspective view of an end of the embodiment of an inflatable bolt and reinforcing structure shown in FIGS. 2 and 3;

FIG. 5 represents a cross-sectional view of an embodiment of an inflatable bolt and reinforcing structure prior to inflation of the bolt;

FIG. 6 represents a cross-sectional view of the embodiment shown in FIG. 5 subsequent to inflation of the bolt;

FIG. 7 represents a cross-sectional view of another embodiment of an inflatable bolt and reinforcing structure prior to inflation of the bolt;

FIG. 8 represents a cross-sectional view of the embodiment shown in FIG. 7 subsequent to inflation of the bolt;

FIG. 9 represents a perspective view of a further embodiment of an inflatable bolt and reinforcing structure prior to inflation of the bolt;

FIG. 10 represents a perspective view of the embodiment shown in FIG. 9 subsequent to inflation of the bolt;

FIG. 11 represents a perspective view of an embodiment of a clamp for securing an inflatable bolt and reinforcing structure together and to a bushing of the inflatable bolt;

FIG. 12 represents an end view of the embodiment of the clamp shown in FIG. 11;

FIG. 13 represents a cross-sectional view of the embodiment of the claims shown in FIG. 12 along the line 13-13;

FIG. 14 represents a perspective view of an embodiment of a clamp insert;

FIG. 15 represents an end view of the clamp insert shown in FIG. 14;

FIG. 16 represents a longitudinal cross-sectional view of the clamp insert shown in FIG. 15 along the line 16-16;

FIG. 17 represents a perspective view of an embodiment of a clamp ring;

FIG. 18 represents an end view of the embodiment of the clamp ring shown in FIG. 17;

FIG. 19 represents a cross-sectional view of the embodiment of the clamp ring shown in FIG. 18 along the line 19-19;

FIG. 20 represents a perspective view of an embodiment of a clamp cup;

FIG. 21 represents an end view of the embodiment of the clamp cup shown in FIG. 20; and

FIG. 22 represents a cross-sectional view of the embodiment of the clamp cup shown in FIG. 21 along the line 22-22.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Inflatable bolts may have limited shear strength and stiffness as compared to solid, non-inflatable bolts and/or bolts utilizing grout and/or resin. Loading to a rock bolt may also include sliding of fracture planes inside the walls or ceiling. Such fracturing can impose large shear loading to bolts, particularly to the thin walled material utilized in the inflatable member. Divergently moving planes of rock will apply force in different directions to directly adjacent regions of the inflatable bolt. If shear loading is not resisted adequately the bolt can deform excessively in the shear and fail. This is a very dangerous situation because not only is a failed bolt no longer bearing load, but failure of a bolt in a rock formation is difficult or impossible to detect. The thin walled material utilized to form inflatable bolts may also result in the bolts having low stiffness.

Embodiments of the reinforcement structure may provide enhanced shear and/or tensile resistance for inflatable bolts. The reinforcement structure may increase shear strength and/or shear stiffness. In fact, the reinforcement structure may dramatically increase strength of inflatable blots, such as on the order of about doubling the shear and tensile strength. The reinforcement provides additional strength along the length of the thin walled inflatable section.

Embodiments of the reinforcement do not require resin or grout. Additionally, embodiments of the reinforcement may be utilized with existing inflatable bolts. Embodiments of the reinforcement may be installed on existing inflatable bolt designs before or during installation of the bolts.

Embodiments of the reinforcing structure may increase tensile strength of an inflatable bolt far beyond industry standard for a given bore hole size. A bolt with increased tensile strength and stiffness can reduce tunnel convergence. Additional shear capacity can prevent internal rock shifting and resulting bolt failure due to shear. In some cases, the capacity to withstand shear and tensile forces may be doubled as compared to inflatable bolts with reinforcement.

Embodiments of the reinforcement may include at least one reinforcement element arranged on an exterior surface of an inflatable bolt. Some embodiments of the reinforcement may include at least one strand arranged on the exterior of the inflatable bolt. For example, the strand could include a wire, rope, rod, cylinder or cable. The strand could be rigid or non-rigid. Additionally, the strand could be hollow or solid. If the strand is hollow, it could be filled with a material. The strand could be a single element or made up of many strands, such a rope.

Additionally, the strand could be slack, to provide passive support, or taught, to as to be pre-tensioned upon inflation of the bolt to provide active support. The strand could be made of steel, carbon fiber or any other suitable material. If steel is utilized, the steel could be high-tensile steel wire. One example is CrSi wire. Alternatively, a steel rope or cable could be utilized. If carbon fiber is utilized, the carbon fiber could be in the form of a rope. Any suitable material could be utilized in any suitable form to provide additional tensile and/or shear reinforcement. Also, more than one strand could be utilized. The strands could all be of the same material or differing materials. Similarly, the strands could all have the same form or be of different forms.

Any strand typically will be thicker than the thin walled material utilized in the inflatable bolt. This will make the strand better able to resist shear and tensile forces. Additional strength may come from forming the strand of multiple elements or strands to form a rope or cable. A thicker and stronger material will be much better able to resist shear forces such as from fracturing planes. The strand may also be better able to resist tensile forces applied to an inflatable bolt by shifting rock formation.

If at least one strand is utilized, the strand could be attached to the inflatable bolt. Typically, when deflated, an inflatable bolt has a shape that is generally U-shaped or a horseshoe shape. A reinforcing strand could be arranged anywhere about the exterior surface of the inflatable bolt. Typically, a reinforcing strand is arranged in the U or horseshoe shape. This may help to maintain the position of the strand as the bolt is inflated. FIG. 5 illustrates a cross-sectional view of an embodiment of a strand arranged with an inflatable bolt prior to inflation of the bolt.

FIGS. 1-6 illustrate one embodiment of a reinforcement structure and an inflatable bolt. The reinforcement structure according to this embodiment includes a strand 1. Typically, an inflatable bolt includes a bushing 3 at each end of an inflatable segment 4. The reinforcing structure 1 could extend through the bushings as shown in FIGS. 1-4. Alternatively, the reinforcement structure may extend to the bushings 2 and 3. It is possible that the reinforcement structure may not extend all the way to the bushings. The reinforcement structure may extend between the bushings. It is also possible that ends of the reinforcement structure may be secured differently, such as one end extending through the bushing and one end extending to the bushing.

FIG. 5 illustrates a cross-sectional view of the embodiment shown in FIGS. 1-4 prior to inflation of the bolt. FIG. 6 illustrates the embodiment subsequent to inflation of the bolt by introducing an inflation medium into the interior 4 a of the inflatable member. In FIG. 6, the rock formation 5 would surround and be in contact with the inflatable member and the reinforcement member.

An alternative embodiment of the reinforcement member is shown in FIGS. 7-10. The alternative embodiment may include a tube or sleeve 6 that extends at least partially around the inflatable member. The embodiment of the sleeve shown in FIG. 7 does not extend entirely about the bolt. Therefore, the ends 7 of the sleeve 6 form a slit 8. As the inflatable bolt is inflated, the slit permits the sleeve to expand. When the expandable bolt is expanded in a bore hole, the split tube opens to allow expansion and is trapped between the expandable bolt and a wall of the borehole. FIG. 8 illustrates an embodiment of a sleeve extending around an inflatable bolt. With the bolt inflated to a maximum inflated state, the sleeve typically extends about at least one-half of the circumference of the inflatable bolt. The slit tube sleeve may be slipped over the length of the expansion tube.

FIGS. 9 and 10 illustrate an embodiment of a reinforcing sleeve 6 that is a complete cylinder that extends entirely around the inflatable member. The sleeve includes a mesh structure. As the bolt is inflated, the mesh expands.

The sleeve or tube may be solid or a mesh. A number of different materials may be utilized to form the sleeve or tube. For example, the sleeve or tube could be made of steel, fiberglass or carbon fiber. The sleeve or tube could be made of a woven material. A number of other high-strength materials could also be utilized. If a bolt is exposed to shearing forces, the tube or sleeve provides additional shear capacity.

The reinforcement structure could be secured to the inflatable bolt. For example, the reinforcement could be glued to the inflatable bolt. The reinforcement structure could also be welded to the inflatable bolt. Securing the reinforcement structure to the inflatable bolt could provide additional shear resistance. As the inflatable element is inflated, the reinforcement member may be held in place by friction between the rock on the surface of the hole and the inflatable member.

The bushings may at least partially clamp the reinforcement structure to the inflatable bolt. The reinforcement structure could be secured only to the bushings and not to the inflatable bolt. The reinforcement structure may be held in place at least partially by forces between the bolt and the wall of the hole in which the bolt and reinforcement structure are inserted. Additionally or alternatively, the reinforcing structure could be mechanically fastened to at least some portion of the inflatable bolt structure.

If the reinforcement structure is mechanically fastened, it could be at least partially fastened with a friction or knot interlock. Such connections could provide both shear and tensile strength. If the reinforcement structure extends protrudes into or extends through the end bushings. The mechanical friction fastener may be engaged to the strand after insertion in the bushing.

The mechanical faster may be configured to engage the end bushings as the bolt elongates under load. As such, the mechanical fasten may apply the tensile loading capacity of the reinforcing structure between the end bushings. At the same time, holding the reinforcing structure in place provides shear load capacity. Additionally, a load condition causing a large shear deformation may result in the reinforcing structure connecting the bushings through a longer route, thereby incurring an addition tension force between each bushing, compressing the entire bolt. If the reinforcing structure is non-rigid, such as a cable, the reinforcing structure may be slack for passive support upon inflation, or taught then pre-tensioned upon inflation for active support.

FIGS. 11-22 illustrate elements of an embodiment of a friction fastener to mechanically fasten a reinforcing structure to the bushing. Along these lines, FIG. 11 illustrates a complete assembled fastener. This embodiment is a cable clamp including a cup 9, a clamp 10, and a clamp ring 11. FIG. 9 illustrates an end view of the embodiment shown in FIG. 8 and FIG. 10 illustrates a cross-sectional view.

The clamp 10 directly contacts the reinforcing structure. Typically, the reinforcing structure secured by such an embodiment of a fastener is a strand. The strand extends into or through the clamp. The clamp 10 has an interior diameter that is slightly larger than a diameter of the strand. This permits the strand to slide through the clamp.

The clamp includes at least one slit 6 a that extends through the thickness of the clamp body and partially along the length of the clamp body. As the clamp is drawn into the cup 9, the at least one slit 12 collapses around the strand, thereby clamping the strand. This may happen as the fastener is assembled and/or as the strand is placed in tension during use. Additionally, as shown in FIG. 16, the outer diameter of the clamp may be larger at the end 13 including the opening of the at least one slit and narrower at the other, opposite, end 14. This may also cause the at least one slit 12 to collapse as the clamp is drawn into the cup 9.

The clamp 10 is received by a cup 9. The cup 9 has an outer surface 15 that may be contoured at one end. For example, the embodiment shown in FIGS. 11, 13, 21 and 22 is rounded at one end 16. This may facilitate engaging the cup 9 with the bushing 2, 3. The rounded surface 17 may also provide a joint that permits the fastener and strand to move as the rounded surface of the cup moves on the surface of the bushing opening. The remaining portion 18 of the exterior surface of the typically has a diameter similar to the diameter of the bushing. This may facilitate insertion of the structure in a hole.

The interior surface 19 of the cup 9 may include different contoured portions. For example, the interior surface may include an angled portion 20 that is angled similar to the exterior surface of the clamp 10. This may facilitate insertion of the clamp and fixing of the clamp in the cup. The interior surface of the cup may also include a curved portion 21. The curved portion may help to hold the clamp once inserted. The angled and curved portions of the interior surface of the cup may compress the clamp as the clamp is drawn into the cup to help clamp the strand, particular, as the inflatable bolt and strand experience tension and shear forces.

The fastener may also include a clamp ring 11. As shown in FIGS. 11 and 13, the clamp ring 11 may be fit around the portion of the clamp that extends from the cup 9. The clamp ring 11 may have an internal surface 22 having a diameter that is smaller than at least a portion of the external diameter of the clamp 10. The clamp 10 may be inserted into the clamp ring 11 and then into the cup 9. Openings of the clamp ring 11 may include a chamfer 23 to facilitate inserting the clamp into the clamp ring. As the clamp is inserted into the cup, the at least one slot in the clamp ring will be collapsed to clamp the strand.

Rather that fixing a tensile strand to the end bushings, a tensile strand may be fixed only through inflation of the inflatable bolt and may not be fixed to end bushings. Along these lines, the tensile strand 1 may be routed through the inflation profile 4 such that the strand does not protrude into the end bushings 2 and 3. The strand may be glued or mechanically fastened in place for ease of shipping or installation. Such a strand may provide a significant increase in the shear capacity of the bolt in the event of a load condition causing large shear deformation.

The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention, but as aforementioned, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments. 

1. An inflatable rock bolt, comprising: an expansion tube; a bushing arranged at each end of the expansion tube; and at least one reinforcing member arranged outside the expansion tube, the at least one reinforcing member comprising at least one of a strand extending along the expansion tube or a sleeve at least partially surrounding the expansion tube, wherein the at least one reinforcing member extends between the bushings.
 2. An inflatable rock bolt according to claim 1, wherein the at least one reinforcing member extends through or to the bushing arranged at each end of the expansion tube.
 3. The inflatable rock bolt according to claim 1, wherein the strand comprises at least one of a wire or a rope.
 4. The inflatable rock bolt according to claim 2, wherein the strand comprises steel wire, steel rope or carbon fiber rope.
 5. The inflatable rock bolt according to claim 4, wherein the steel is high tensile.
 6. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is adhered to the expansion tube.
 7. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is welded to the expansion tube.
 8. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is mechanically fastened to the expansion tube.
 9. The inflatable rock bolt according to claim 8, wherein the at least one reinforcing member is fastened with a friction or knot interlock.
 10. The inflatable rock bolt according to claim 8, further comprising: a mechanical coupling configured to engage the at least one reinforcing member.
 11. The inflatable rock bolt according to claim 10, wherein the mechanical coupling engages the bushings when tension is applied to the bolt.
 12. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member provides at least one of shear and tensile reinforcement.
 13. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is anchored to the bushings.
 14. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is clamped by the bushings.
 15. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member protrudes through the bushings.
 16. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member protrudes into the bushings.
 17. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is not secured to the bushings and is fixed in place through friction between the expansion tube and a formation in which the bolt is inserted.
 18. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member comprises a shroud that extends at least half way around the exterior surface of the expansion tube with the expansion tube in an expanded state or contracted state.
 19. The inflatable rock bolt according to claim 18, wherein the shroud is made of carbon fiber.
 20. The inflatable rock bolt according to claim 1, wherein the at least one reinforcing member is at least partially secured by friction between the inflatable member and a wall of a hole in which the rock bolt is inserted.
 21. A method for reinforcing an inflatable rock bolt, the method comprising: extending at least one reinforcing member along an exterior surface of an expansion tube, wherein the at least one reinforcing member comprises at least one of a strand extending along the expansion tube or a sleeve at least partially surrounding the expansion tube; arranging a bushing at each end of the expansion tube, wherein the at least one reinforcing member extends between the bushings; inserting the expansion tube and the at least one reinforcing member into a hole; and expanding the expansion tube, thereby frictionally clamping the at least one reinforcing member between the expansion tube and a wall of the hole in which the bolt is inserted.
 22. The method according to claim 21, wherein the at least one reinforcing member is slack before expanding the expansion tube.
 23. The method according to claim 21, further comprising: pre-tensioning the at least one reinforcing member prior to expanding the expansion tube.
 24. The method according to claim 21, wherein extending the at least one reinforcing member comprises extending at least one of a wire or a rope along the exterior surface of the expansion tube.
 25. The method according to claim 21, further comprising: adhering the at least one reinforcing member to the expansion tube.
 26. The method according to claim 21, further comprising: welding the at least one reinforcing member to the expansion tube.
 27. The method according to claim 21, further comprising: mechanically coupling the at least one reinforcing member to the expansion tube.
 28. The method according to claim 27, wherein the at least one reinforcing member is coupled with a friction or knot interlock.
 29. The method according to claim 27, wherein the mechanical coupling engages the bushings when tension is applied to the bolt.
 30. The method according to claim 21, further comprising: anchoring the at least one reinforcing member to the bushings.
 31. The method according to claim 30, wherein the at least one reinforcing element is clamped by the bushings.
 32. The method according to claim 21, wherein the at least one reinforcing member is arranged to protrude through the bushings.
 33. The method according to claim 21, wherein the at least one reinforcing member is arranged to protrude into the bushings.
 34. The method according to claim 21, wherein the at least one reinforcing member extends through or to the bushing arranged at each end of the expansion tube.
 35. The method according to claim 21, wherein the at least one reinforcing member is not secured to the bushings and is fixed in place through friction with the expansion tube.
 36. The method according to claim 21, wherein extending at least one reinforcing member along an exterior surface of an expansion tube comprises wrapping a shroud at least half way around the exterior surface of the expansion tube.
 37. The method according to claim 36, wherein the shroud extends at least half way around the exterior surface of the expansion tube with the expansion tube in an expanded state or contracted state. 